LPJ, I don't mean to be critical, but you've squandered a never-to-be-repeated dual opportunity to butcher a debt collector (as is perfectly right and proper, you will agree) and to terrorise your neighbour into submission.
It would have been perfect;
a) it was a debt collector
b) it was in the wrong
c) you've always wanted to use that strimmer on someone. Anyone. Don't try to pretend otherwise.
d) thereafter, every time your neighbour considered getting stroppy about something, he'd think; Hang on, remember what he did to that other poor bastard.
Edit; although come to think of it, if your neighbour's such a shitsmear, chances are that there'll be other debt collectors to come. You'll know what do do next time, so don't fuck it up again. Try to get some pics, too.